Well first you have to be made of circuitry components such as transistors, resistors, capacitors, wires, silicon, and of course the ever popular silver/lead solder.
What are you trying to ask? You want to become a Human Lie Detector? You will not get a 100% accuracy reading but if you study the interaction of people you can pick up a few things. Most people I have found look anywhere but in directly in your eyes when they are lying to you. Body Language is a big factor.